In December, 1992 an industry-wide standard protocol for Analog Display Services Interface (ADSI) was completed by Bell Communications Research Inc. (Bellcore specifications) to serve as a standard for voice and display (data) information to be transmitted between subscriber display-based terminals and telecommunications switches or servers over the existing copper telephone lines. This standard protocol also defines the formats for the large scrollable displays and softkeys to support new enhanced, interactive, services.
Typical of the interactive subscriber terminals (telephone sets) designed to support the ADSI protocol is the one described in U.S. patent application Ser. No. 354,599 filed on Dec. 13, 1994 in the name of William V. Pezzullo et al and entitled "Screen-Based Telephone Set For Interactive Enhanced Telephony Service". This copending application is incorporated herein by reference.
The subscriber terminal described in the pending application has a relatively large scrollable display and context-sensitive softkeys which enable the terminal to make full use of services typically provided by telephone operating companies, as well as those services provided by enhanced service providers (ESP) delivering third party services and applications through the PSTN (public switched telephone network).
Enhanced service providers (ESPs) are the second major source of ADSI-based services. ESP applications are driven by information downloaded to the terminal from a server--for example, an interactive voice-responsive system located in a bank.
The terminal supports the ADSI protocol which includes the concept of FDM (feature download management) software scripts which can control the display and the softkeys and cause the terminal to go on-hook, off-hook and dial numbers. The terminal also supports an extension to the Bellcore specifications which allows a server to download an FDM script without any intervention by the subscriber. This capability, called Server Initiated Download or ADSI On-Hook Alerting for Automatic Feature Download, requires access to the Tip and Ring of the telephone line connected to the target subscriber terminal while the terminal is on-hook. The downloading of the FDM script is carried out unobtrusively--i.e., without ringing the telephone. This Server Initiated Download capability is not universally available on all types of Central Office Switching equipment and requires specialized connections from the FDM download server to the Central Office Switching equipment.